Duration of development and number of nymphal instars are differentially regulated by photoperiod in the cricket Modicogryllus siamensis (Orthoptera: Gryllidae)

Norichika Taniguchi,Kenji Tomioka

doi:10.14411/eje.2003.043

Abstract

The effect of photoperiod on nymphal development in the cricket Modicogryllus siamensis was studied. In constant long-days with 16 hr light at 25Â°C, nymphs matured within 40 days undergoing 7 moults, while in constant short-days with 12 hr light, 12~23 weeks and 11 or more moults were necessary for nymphal development. When nymphs were transferred from long to short day conditions in the 2nd instar, both the number of nymphal instars and the nymphal duration increased. However, only the nymphal duration increased when transferred to short day conditions in the 3rd instar or later. When the reciprocal transfer was made, the accelerating effect of long-days was less pronounced. The earlier the transfer was made, the fewer the nymphal instars and the shorter the nymphal duration. The decelerating effect of short-days or accelerating effect of long-days on nymphal development varied depending on instar. These results suggest that the photoperiod differentially controls the number of nymphal instars and the duration of each instar, and that the stage most important for the photoperiodic response is the 2nd instar.

Highlights

Most insects in temperate zones have life cycles highly adapted to seasonal change
The life cycles of crickets are known to be under photoperiodic control
The results show that photoperiod differentially controls the number of nymphal instars and the duration of development, and that the stage most important for the photoperiodic response is the 2nd instar

Summary

Introduction

Most insects in temperate zones have life cycles highly adapted to seasonal change. Photoperiod is the most important environmental cue controlling seasonal life cycles. The life cycles of crickets are known to be under photoperiodic control. Nymphal development of crickets that overwinter as eggs, such as Teleogryllus emma, Dianemobius mikado and D. nigrofasciatus, is accelerated by short day or intermediate photoperiods (Masaki, 1967, 1973, 1979). These responses are thought to determine the time of adult emergence and oviposition of diapause eggs in autumn. In univoltine species that overwinter as nymphs, such as Gryllus campestris and Pteronemobius nitidus, short-days experienced in the early instars induce and maintain diapause but long-days experienced after a period of short-days terminate diapause (Masaki & Oyama, 1963; Ismail & Fuzeau-Braesch, 1972, 1976; Masaki, 1972). The mechanism by which photoperiod controls the nymphal development in bivoltine species has not been studied in detail

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